In recent years, one of the key issues in the aircraft industry is to improve the fuel efficiency of aircrafts from the viewpoint of reduction of aircraft operation costs as well as environmental conservation. Accordingly, reduction in power loss of planetary gear systems for use in aircraft engines is also required.
Conventionally, such a planetary gear system includes a mechanism for supplying lubricating oil to the gears for the purpose of lubricating and cooling down the gears. Here, agitation resistance of the lubricating oil that is supplied around the gears is one of the main causes of power loss in the planetary gear system. One of the techniques proposed for reducing such agitation resistance of lubricating oil is, for example, as follows: lubricating oil that has been supplied to a mesh position between a sun gear and a planet gear is discharged axially by utilizing rotation of the planet gear which is a double helical gear, and a baffle (a barrier) is provided between adjacent planet gears, so that generation of a swirl flow due to interference of flows of lubricating oil that are generated around the adjacent planet gears is suppressed (see Patent Literature 1, for example).